Fix declaration emit synthesizing extensionless import() specifier under allowImportingTsExtensions + nodenext

[RyanCavanaugh]

When using allowImportingTsExtensions: true with .ts-extension relative imports under module: nodenext, declaration emit was generating invalid extensionless import() type references for node_modules packages — import("mylib/lib/Box") instead of import("mylib/lib/Box.js") — causing TS2307 errors in the emitted .d.ts.

Root cause

GetAllowedEndingsInPreferredOrder in preferences.go checked the ESM+NodeNext special case as:

if syntaxImpliedNodeFormat == core.ResolutionModeESM && moduleResolutionIsNodeNext {

TypeScript 6 uses (syntaxImpliedNodeFormat ?? impliedNodeFormat), falling back to the file's implied node format when syntaxImpliedNodeFormat is not provided. The Go port was missing this fallback.

When tryGetModuleNameAsNodeModule calls with ResolutionModeNone, the ESM check was always false, yielding [TsExtension, Minimal, JsExtension, Index] instead of the correct [TsExtension, JsExtension]. With Minimal before JsExtension, processEnding picked the extensionless form for .d.ts declaration files.

Fix

• internal/modulespecifiers/preferences.go: When syntaxImpliedNodeFormat is ResolutionModeNone, fall back to resolutionMode (the file's default) before the ESM+NodeNext check — matching TypeScript's ?? semantics.

• testdata/tests/cases/compiler/declarationEmitImportSpecifierWithTsExtensionRelativeImport.ts: Regression test covering the exact repro: ESM package, .ts-extension relative import chain, node_modules subpath with .js extension, verified mod.d.ts output is now import("mylib/lib/Box.js").Box<string> with no TS2307.

• Fixes Behavior difference: declaration emit synthesizes extensionless import() specifier under allowImportingTsExtensions, invalid in nodenext #4616

[Copilot]

Pull request overview

Fixes declaration emit to preserve .js package subpath extensions under NodeNext when TypeScript-extension imports are allowed.

Changes:

• Falls back to the file’s resolution mode when no syntax-implied mode exists.
• Adds regression coverage and declaration/type/symbol baselines.

Show a summary per file

File	Description
internal/modulespecifiers/preferences.go	Implements the upstream resolution-mode fallback.
testdata/tests/cases/compiler/declarationEmitImportSpecifierWithTsExtensionRelativeImport.ts	Adds the regression scenario.
testdata/baselines/reference/compiler/declarationEmitImportSpecifierWithTsExtensionRelativeImport.js	Verifies .js in declaration emit.
testdata/baselines/reference/compiler/declarationEmitImportSpecifierWithTsExtensionRelativeImport.types	Records inferred types.
testdata/baselines/reference/compiler/declarationEmitImportSpecifierWithTsExtensionRelativeImport.symbols	Records symbols.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0
• Review effort level: Medium

[RyanCavanaugh]

This is a redo of #4649 but now GitHub API is down 🙁